1. Technical Field
The invention relates to waterproof roofing systems and in particular to an improved seam for overlapping waterproof covering membranes. Even more particularly, the invention relates to such a lap seam and method of forming the same which eliminates the use of solvents and gases for cleaning the edges of the membrane adjacent the seam before applying a bead or layer of sealant.
2. Background Information
The use of waterproof membranes formed of various elastomeric compositions such as EPDM, are gaining wide acceptance in the roofing industry. These membranes eliminate the use of ballast gravel and asphalt impregnated sheets as the waterproof covering and their inherent disadvantages, such as increased cost and weight. However, one of the problems with the use of such elastomeric waterproof membranes is the ability to provide a satisfactory and long-lasting seam where two adjacent sheets of the membranes are joined, usually in a lapped seam arrangement.
Various types of seams and sealing arrangement therefor are provided, as well as methods of installing the same, in order to provide a satisfactory seam, both for the roofing industry and for other types of products, wherein sheets of waterproof material are joined together. Examples of such prior art seam constructions and forming methods are shown in the following patents.
U.S. Pat. No. 3,770,556 discloses a closure sleeve that is adhesively joined together in an overlapped relationship together with means to prevent the overlapping edge from peeling. The sleeve is joined by means of an adhesive layer and a cover sheet which is adhesively bonded over the overlapped edge. A foil cover sheet, a plastic cover sheet and a fabric cover sheet then are used.
U.S. Pat. No. 4,289,552 discloses a method for welding together thermoplastic sheets in an overlapped relationship. A double faced adhesive holds a pair of thermoplastic sheets together until a welding bead in a thermoplastic state is applied to the seam from an applicator.
U.S. Pat. No. 4,379,114 discloses the bonding of two waterproof sheets to form a joint that has a curved wave configuration in cross section. Cure tape is positioned between the waterproof sheets and a press member of a cushion material that facilitates the curved configuration of the final lap joint is used. Heat and pressure then are applied to the overlapped sheets to cause the cure tape to deform into the desired configuration.
U.S. Pat. No. 4,445,955 discloses a method for joining together thermoplastic sheets in an overlapped relationship in which the sheets are welded together by an extruded thermoplastic material.
U.S. Pat. No. 4,654,098 is believed to be one of the closest known prior art to the present invention. This patent discloses a method for joining sheets of heat resistant fabric in an overlapped relationship. The marginal edge portions of the sheets are coated with an adhesive layer and the two sheets are then joined afterwhich an overcoat of a thermoset urethane polymer is applied over the overlapped sheet onto the adjacent sheet. The overcoat covers a portion of the adhesive coated marginal edge of the seam.
U.S. Pat. No. 4,849,268 also is of some interest with respect to the present invention in that it discloses a liquid containment system that is formed by adhering together individual membrane sheets in an overlapping relationship to form a lap seam. The membranes have cement layers that bond to each other afterwhich a bead of sealant is positioned at the outermost edge portion of the seam between the membranes.
Another common method and lap seam construction for many waterproof membranes used in a roof covering of which the present invention is an improvement thereof, consists of initially securing the lapped edges of the membranes together by use of an intervening sealant. Next, the matted talc or mica which is on the roofing membrane is removed by scrubbing the edges adjacent the seam with unleaded gas or a compatible solvent, in order that a caulking bead or sealant, which is next applied along the seam, will bond to the edge portions of the membrane adjacent the formed seam. Although this method provides a satisfactory seam, it is preferable for many applications to eliminate the use of a cleaning solvent used to clean the area adjacent to the seam, due to its possible contamination of the lap seam adhesive occasionally resulting in wrinkling and opening of the seam and reduction in the seam strength. Furthermore, the elimination of some solvents is desirable because of its contact with roofing personnel, environmental considerations and its affect on both the lap seam adhesive and externally applied lap sealant. The application of these cleaning solvents also involves additional cost for the solvent, and the labor for applying the same along the lap seam.
Therefore, the need exists for an improved lap seam and method of forming the seam at the application site, preferably on a roof using elastomeric covering membranes, which eliminates the use of a cleaning solvent along the lap seam, while providing a lap seam of increased strength and field life.